JP2751072B2 - Valve timing control device for DOHC engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a valve timing control device for controlling the timing of opening and closing an intake / exhaust valve in a DOHC (double overhead camshaft type) engine.

(Background of the Invention) In a four-stroke engine emphasizing high-speed output,
To increase the output at high speed, it is conceivable to increase the valve lift and the valve opening angle (increase the cam operating angle). In this case, idling becomes unstable.
In particular, a plurality of intake valves and exhaust valves are provided for one cylinder,
For example, in an engine with 4 or 5 valves,
Since this is substantially equivalent to an increase in valve overlap, the influence of air-fuel mixture blow-through or interference between the intake and exhaust systems increases, and the idling operation becomes more unstable. Therefore, it is conceivable to reduce the valve overlap while increasing the valve operating angle,
In this case, it is necessary to delay the entire opening period of the intake valve, and the closing timing of the intake valve is delayed. For this reason, at the time of low and medium speeds, there arises a problem that the air is blown back, the filling effect is reduced, and the low-speed torque is reduced.

Therefore, there has been proposed a valve timing control system in which the intake valve and the exhaust valve are of a two-headed camshaft type that can be independently opened and closed by separate camshafts, and the camshaft on the intake side is advanced at low, medium, and high loads. In this proposed device, a piston is engaged between the intake side camshaft and the timing belt pulley by a spiral spline, and the phase of the camshaft is changed by moving the piston by hydraulic pressure. It is. That is, the camshaft is switched between two phase positions by disconnection and connection of hydraulic pressure.

However, it has been found that in an actual engine, the valve overlap required for stabilizing the idling and the valve overlap required for increasing the torque at a high speed are not always the same.

(Object of the Invention) The present invention has been made in view of the above circumstances, and provides a valve timing control device for a DOHC engine that can obtain an optimal valve timing and valve overlap according to an operating state. The purpose is to do.

(Constitution of the Invention) According to the present invention, an object of the present invention is to provide a DOHC engine having a plurality of camshafts that open and close an intake valve and an exhaust valve separately, with reference to an advance position at the time of high-speed rotation of the engine. While the exhaust camshaft is advanced except during high-speed operation,
This is achieved by a valve timing control device for a DOHC engine characterized in that the intake camshaft is advanced at low speed and high load.

(Embodiment) FIG. 1 is a plan view of one embodiment of the present invention, FIG. 2 is a timing belt layout thereof, FIG. 3 is an enlarged sectional view of a timing switching mechanism, and FIG. FIG. 3B shows the state at the time of excitation. 4A and 4B are cross-sectional views showing the operation of the control valve of the timing switching mechanism, FIGS. 5A to 5B are diagrams showing the advance angle characteristics of each cam shaft for different operation states, and FIG. 6 is a diagram showing both cam shafts. FIG. 4 is an advanced angle control map diagram of FIG.

In FIG. 2, reference numeral 10 denotes a cylinder body, 12 denotes a cylinder head, and 14 denotes a head cover.
An intake-side camshaft 16 and an exhaust-side camshaft 18 are held between the mating surfaces of the camshaft 16 and the head cover 14. The intake-side camshaft 16 has three cams 16a for one cylinder, and the exhaust-side camshaft 18 has two cams 18a. The cams 16a and 18a open and close the intake valve and the exhaust valve via valve lifters, respectively. That is, 3 for one cylinder
Five-valve direct acting type 2 having two intake valves and two exhaust valves
It is an overhead camshaft engine. In FIG. 1, reference numeral 20 denotes a cylinder bore, and reference numeral 22 denotes a spark plug position.

Timing switching mechanism on the left end of each camshaft
24, 26 are installed. Since these mechanisms 24 and 26 have exactly the same structure, only one of them will be described.

In FIGS. 3A and 3B, reference numeral 28 denotes a bearing for the camshaft 16. Engine bearing oil of a predetermined pressure is guided from a lubricant main gallery (not shown) to the bearing 28.
The annular oil passage 30 and the radial oil passage 32 formed in the shaft 16 guide the bolt 16 to a bolt hole 34 on the center line of the cam shaft 16. 36 is an inner cam body and 38 is an outer cam body. The inner cam body 36 is fixed to the end of the cam shaft 16 by bolts 40. That is, the bolt 40 penetrates the inner cam body 36 and is screwed into the bolt 34. Reference numeral 42 denotes a knock pin for preventing the displacement between the inner cam body 36 and the cam shaft 16. The outer cam body 38 is formed in a cylindrical shape, one end of which is slightly rotatably held by a flange portion of the inner cam body 36, and a ring-shaped seal is provided between the other end and the outer peripheral edge of the inner cam body 36. Block 44 is oil-tightly mounted. A cover 46 is fixed to the seal block 44, and an oil chamber 48 is formed between the cover 46 and the inner cam body 36. The bolt 40 has an oil hole 40a formed therein.
, A lubricating oil of a predetermined pressure is led.

A cylindrical piston 50 is mounted between the inner and outer cam bodies 36 and 38, and the piston 50 and the cam bodies 36 and 38 are meshed with each other by a spiral spline. This piston 50 is also returned to the seal
While returning to the side is provided, the oil pressure in the oil chamber 48 is guided between the piston 50 and the seal block 44 via the small hole 54.

The oil pressure in the oil chamber 48 is controlled by a control valve 56 and an electromagnetic solenoid 58 provided on the cover 46.
The valve 56 includes a case 60, a slider 62, and a return spring 64, as shown in FIGS. 4A and 4B. The case 60 and the slider 62 are provided with oil holes 60a and 62a, respectively.These oil holes 60a and 62a communicate with each other at the return position of the slider 62, and allow oil in the oil chamber 48 to flow as shown by an arrow in FIG. 4A. Guide out of the switching mechanism 24. For this reason, the oil pressure in the oil chamber 48 decreases. Electromagnetic solenoid
The plunger 58a of 58 faces the slider 62, and the excitation of the solenoid 58 causes the plunger 58a to protrude and
Press 2. In this state, the slider 62 closes the oil hole 60a of the case 60 as shown in FIG. 4B. As a result, the oil pressure in the oil chamber 48 increases, and the increased oil pressure pushes the piston 50 to the right in FIG. Since the piston 50 is engaged with the inner and outer cam bodies 36 and 38 by the spiral spline, the inner and outer cam bodies 36 and 38 are relatively rotated by the movement of the piston 50.

The timing switching mechanisms 24, 26, configured as described above,
Pulley teeth 66, 66A are formed on the outer cam bodies 38, 38A (FIG. 2), and a timing belt 68 is wound around both pulley teeth 66, 66A. That is, the rotation of the crankshaft 70 is transmitted to the pulley teeth 66 and 66A via the belt 72, the first intermediate shaft 74, the belt 76, the second intermediate shaft 78, and the belt 68. Thus, the outer cam bodies 38 and 38A are timing pulleys around which the timing belt 68 is wound.

1 and 2, reference numeral 80 denotes a rotation angle sensor, which electrically or magnetically detects the passage of a projection 82 provided on the outer cam body 38A of one of the switching mechanisms 26, and detects the ignition timing of the ignition plug. It is.

Electromagnetic solenoids 58, 58A for timing switching mechanisms 24, 26
Is controlled by a control circuit 82 such as a microcomputer so that the phases of the camshafts 16 and 18 have the characteristics shown in FIGS. That is, the switching mechanism 24 on the intake side
Indicates that when the solenoid 58 is not energized, the intake valve lift becomes maximum at a phase delayed by an angle (c) from TDC (top dead center) (5th
(See A, C, and D diagrams.) Also, at the time of excitation, the angle from TDC (d)
The intake valve lift is set to be maximum in the delayed phase ((c)> (d)) (FIG. 5B). In addition, the exhaust-side switching mechanism 26 maximizes the exhaust valve lift in a phase advanced by an angle (a) from the top dead center when the solenoid 58A is not excited (see FIGS. 5A, 5B, and 5C). The lift becomes maximum at the phase advanced by angle (b) (Fig. 5D). Here, the angles a, b, c, and d are set with the following relationship.

(Ero)> (Ni-ha) (1) The control circuit 82 operates according to the operation program stored in the memory 84. The memory 84 stores the control characteristics shown in FIG. That is, the control circuit 82 receives the engine rotation speed N, the load L detected from the throttle valve opening, and the like, and further receives signals from the rotation angle sensor 80 and the like.
At high speed, only the solenoid 58A of the exhaust side switching mechanism is excited to retard the camshaft 18 from the angle (a) to (b) with respect to TDC. At this time, the valve overlap occurs when the intake and exhaust sides are both de-energized (idle
It increases to C with respect to the valve overlap A at the time of middle speed (Fig. 5C) and at the middle speed (Fig. 5C). At low speed and high load, only the solenoid 58 on the intake side is excited to advance the camshaft 16 from the angle (C) to (D) (FIG. 5B). At this time, the valve overlap B satisfies A <B <C due to the relationship (1).

Since the camshafts 16 and 18 are advanced or retarded as described above, the output at high speed is increased by using a camshaft with a large cam operating angle of the intake and exhaust valves (FIG. 5D). The operation can be stabilized by reducing the valve overlap from C to A at the time of idling or medium speed (FIGS. 5A, C). Further, at low speed and high load (FIG. 5B), the intake cam shaft is advanced to prevent the intake air from returning, thereby increasing the charging efficiency torque and improving fuel efficiency. At this time, since the exhaust camshaft is advanced, valve overlap is reduced, and blow-by of intake air is reduced, so that fuel efficiency can be improved.

(Effect of the Invention) As described above, according to the present invention, based on the advance position at high speed, the exhaust camshaft is advanced except at high speed, and the intake camshaft is advanced at low speed and high load. Because
It is possible to stabilize idling operation and increase torque at low speed and high load while increasing output at high speed, and to obtain optimal valve timing and overlap according to each operation state.

[Brief description of the drawings]

FIG. 1 is a plan view of one embodiment of the present invention, FIG. 2 is a timing belt layout thereof, FIGS. 3A and 3B are enlarged sectional views showing different operation states of a timing switching mechanism, and FIGS. FIGS. 5A to 5D are diagrams showing the advancement characteristics of each camshaft, and FIG. 6 is an advancement control map of both camshafts. 16… Exhaust side camshaft, 18… Intake side camshaft, 24, 26 …… Timing switching mechanism, 82 …… Control circuit,

Claims (1)

(57) [Claims] In a DOHC engine having a plurality of camshafts for opening and closing an intake valve and an exhaust valve separately, the exhaust-side camshaft is operated at a time other than a high-speed operation with reference to an advance position at a high-speed rotation of the engine. DO, while the intake camshaft is advanced at low speed and high load.
Valve timing control device for HC engine.